[PATCH net] sctp: linearize early if it's not GSO

[Marcelo Ricardo Leitner]

Because otherwise when crc computation is still needed it's way more
expensive than on a linear buffer to the point that it affects
performance.

It's so expensive that netperf test gives a perf output as below:

Overhead  Shared Object        Symbol
  69,44%  [kernel]             [k] gf2_matrix_square
   2,84%  [kernel]             [k] crc32_generic_combine.part.0
   2,78%  [kernel]             [k] _raw_spin_lock_bh

And performance goes from 2Gbit/s to 0.5Gbit/s on this test. Doing the
linearization before checksumming is enough to restore it.

Fixes: 3acb50c18d8d ("sctp: delay as much as possible skb_linearize")
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
---

Please consider this to -stable too as v4.7 performance is affected.
Thanks

 net/sctp/input.c   | 11 +++++++----
 net/sctp/inqueue.c | 13 -------------
 2 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 
c182db7d691ff44a52923fb36c9170e49c141c04..69444d32ecda6cd1a4924911172feba89c5ae976
 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -119,7 +119,13 @@ int sctp_rcv(struct sk_buff *skb)
                       skb_transport_offset(skb))
                goto discard_it;
 
-       if (!pskb_may_pull(skb, sizeof(struct sctphdr)))
+       /* If the packet is fragmented and we need to do crc checking,
+        * it's better to just linearize it otherwise crc computing
+        * takes longer.
+        */
+       if ((!(skb_shinfo(skb)->gso_type & SKB_GSO_SCTP) &&
+            skb_linearize(skb)) ||
+           !pskb_may_pull(skb, sizeof(struct sctphdr)))
                goto discard_it;
 
        /* Pull up the IP header. */
@@ -1177,9 +1183,6 @@ static struct sctp_association 
*__sctp_rcv_lookup_harder(struct net *net,
        if ((skb_shinfo(skb)->gso_type & SKB_GSO_SCTP) == SKB_GSO_SCTP)
                return NULL;
 
-       if (skb_linearize(skb))
-               return NULL;
-
        ch = (sctp_chunkhdr_t *) skb->data;
 
        /* The code below will attempt to walk the chunk and extract
diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index 
c30ddb0f31907f57c5ce85b00dbe04260ca1cb2e..6437aa97cfd79f14c633499c2b131389204c435b
 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -170,19 +170,6 @@ next_chunk:
 
                chunk = list_entry(entry, struct sctp_chunk, list);
 
-               /* Linearize if it's not GSO */
-               if ((skb_shinfo(chunk->skb)->gso_type & SKB_GSO_SCTP) != 
SKB_GSO_SCTP &&
-                   skb_is_nonlinear(chunk->skb)) {
-                       if (skb_linearize(chunk->skb)) {
-                               __SCTP_INC_STATS(dev_net(chunk->skb->dev), 
SCTP_MIB_IN_PKT_DISCARDS);
-                               sctp_chunk_free(chunk);
-                               goto next_chunk;
-                       }
-
-                       /* Update sctp_hdr as it probably changed */
-                       chunk->sctp_hdr = sctp_hdr(chunk->skb);
-               }
-
                if ((skb_shinfo(chunk->skb)->gso_type & SKB_GSO_SCTP) == 
SKB_GSO_SCTP) {
                        /* GSO-marked skbs but without frags, handle
                         * them normally
-- 
2.7.4